Almost everybody has a dominant hand that they use, but it's actually a mystery why that is. After all, we can see both of our hands just as well, and there's no built-in reason why one should work better than the other. But some grabby parrots might hold the deep evolutionary reason behind handedness.

Researchers had 322 parrots from 16 different species attempt to pick up an object beneath them with their feet. Because parrots have eyes on the side of their heads, they can't look directly down at the object to help them pick it up. Instead, they have to cock their head to one side or the other to see what they're trying to grab.

The parrots consistently showed a preference for grabbing the object with one foot or the other, and this was in turn reflected by how they cocked their head. For instance, let's say the parrot was right-handed - or, perhaps more accurately, right-footed. In that case, the parrot would almost always cock its head to the left to give its right eye a good view of what was going on below. The right eye would be better equipped to track the movement of the right foot, and so it would grab the object with that foot.

This connection between eyes and handedness isn't something we humans have to worry about, because our eyes are both on the front of our face. But eyes on the side of the head do raise these issues when dealing with things outside the normal field of vision, like the objects beneath the parrots. If our long distant evolutionary ancestors exclusively had eyes on the sides of their heads, that would explain a lot about why handedness evolved and why we humans still possess it.